GENERAL STOCHASTIC UNIT-HYDROGRAPH

Unit hydrographs for a gaged site can be determined from observed events. If several events are used for the derivation, several unit hydrographs result. An averaging procedure must be used to achieve a single representative unit hydrograph. The variability is due to inherent uncertainty in the rainfall processes and to inadequacies in the basic model. It is appropriate to consider the unit hydrograph itself a random function. This paper develops a stochastic expression for the instantaneous unit hydrograph (IUH) based upon the Nash cascade. This conceptual model holds the number of reservoirs constant, while treating the reservoir constant as a random variable. Records of 24 storm events, observed on a 12.2-km2 watershed located in north central Missouri, were studied. The results of the study indicate that the stochastic model can be used to estimate the hydrograph.